The present invention relates to digital x-ray imaging systems, and in particular to a method for stabilizing and optimizing angiogram cine runs and network accessible system for storing and playing back angiography images.
Angiography is a well-known technique that allows real-time detailed visualization, typically in the form of x-ray images, of the cardiac anatomy and function. A typical x-ray angiographic system comprises an x-ray source, an x-ray image intensifier (XRII) and a video camera. The x-ray image intensifier converts the x-ray signal into a light signal which is recorded by a video camera. This technique provides real time video images which, with the injection of a radio-opaque dye, show the motion of the coronary anatomy. The video signal is digitized to yield a series of frames acquired at rates of 15-30 frames/sec. These frames are stored on a hard disk and provide real time playback in the form of a cine angiogram.
In a typical angiographic exam, a large number of images are generated. For example, a single 5 second angiographic cine run generates approximately 16 Megabytes of data (assuming 512xc3x97512 pixel images, 1 byte/pixel, 30 frames/s) and a single diagnostic procedure can involve the acquisition of 5-15 angiographic cine runs. Each angiogram cine run in turn comprises a set of 60 to 125 x-ray images with each cine run providing a detailed view of a different aspect of the cardiac anatomy. Known lossless compression techniques can reduce storage requirements by approximately 60%. Excessive storage requirement is the primary reason why angiograms are typically not stored on-line in Picture Archive Capture Systems (PACS) as is done with many other imaging modalities. Instead the angiographic cine run images are archived on portable media like compact disks.
The angiographic cine runs are played back by a cardiologist in the diagnosis of the patient""s condition. In a medical clinic, a physician will typically view the entire cine run(s) to observe the arteries or ventricle opacify in response to the dye being injected into the patient and then a few more cardiac cycles are viewed when the arteries are fully opacified followed by the loss of the signal due to the interruption of the dye injection. However, if the angiogram cine run is truncated, then displaying the cine run as a repeating movie loop results in poor visualization due to the mis-registration of features of interest between the last frame and first frame in the looped cine run. Each time cine run loop displays the last frame followed by the first frame, the arteries may appear to move abruptly. As a result, the human visual systems of the examining physician (e.g. cardiologist) loses track of a feature of interest for an amount of time which can be significant relative to the time required to display one or two cardiac cycles.
Abrupt motion of the heart from the last to first frame of the movie loop subset can be the result of a poor choice of the last frame relative to the first frame where the last frame corresponds to a very different phase of the cardiac cycle than the first frame. Abrupt motion from last frame to first frame can also be caused by bulk patient motion. Similarly, motion caused by a patient""s breathing together with small amounts of panning which some physicians perform during cine acquisition to reveal structures that are at the edge of the field of view also causes abrupt motion from the last frame to the first frame.
In U.S. Pat. No. 5,293,574 (Roehm et al.), the problem of mis-registration between the last frame and first is avoided by not looping the last frame with the first frame. Instead Roehm discloses showing the frames in temporal order until the last frame of interest is shown and then in reverse temporal order until the first frame of interest is shown and repeating this entire sequence over and over again. While this approach avoids the problem of last frame and first frame registration, it leads to an angiogram cine run where the heart beats conventionally 50% of the time and backwards for the other 50% of the time. It will be appreciated that this does not provide a true rendition of the cardiac physiology.
Accordingly, there remains a need for a method for generating angiogram cine run loops where the problem of mis-registration between the last and first frames is eliminated and a true physiological rendition of the cardiac cycle is provided.
The present invention provides a process for generating and running an angiogram cine run as a continuous movie loop. In another aspect, the present invention also provides a process for extracting a subset of frames from an angiogram cine run and presenting these frames as a movie loop which can displayed continuously.
According to one aspect of the invention, it has been determined that not all the frames in all cine runs generated by an angiographic study are needed to illustrate the salient features of a patient""s case. This is because the cine runs constitute a record of a systematic search for pathologies obtained with differing acquisition geometries allowing close scrutiny of all major coronary artery segments to reduce the possibility of overlooking any lesions. The most relevant views are those that best reveal the lesions of interest.
Accordingly, a more manageable subset of the most relevant frames and cine runs are selected from all the cine runs stored for a patient on removable media (e.g. compact disc (CD) media) and made available on-line. Furthermore, because motion is periodic, providing a subset of frames from one cine run spanning one or two cardiac cycles will often suffice. The extraction of subsets of data from angiographic exams allows physicians and patients to view images from a remote location over the Internet where bandwidth limitations would otherwise restrict the amount of data that can be transmitted within a reasonable delay. According to another aspect of the present invention, a server arrangement for angiogram cine runs is provided. The server is network accessible over a local area network or a wide area network, for example over the World Wide Web (WWW) via the Internet.
The process according to the present invention reduces abrupt motion from the last frame to the first frame by refining the choice of the estimates of first and last frame indices provided by the user and performing image registration so that an a feature of interest, e.g. anatomical features such as arteries or ventricles, will be in nearly the same configuration between the last and first frame.
According to this aspect of the invention, the part of the cardiac cycle is selected which best corresponds to the transition from the last to the first frame. Typically, this occurs when there is the least motion (i.e. end systole and end diastole) because the frame rate is limited and it is more likely that a similar heart configuration will be encountered at some later frame when motion is minimized. It has been found that if an attempt is made to match frames in different cycles when motion is rapid there may not exist a pair of frames that closely resemble each other due to the coarse nature of temporal sampling (i.e. frame rate) and the fact that exact timing for the acquisition of the last and front frames cannot be controlled. Furthermore, it is preferable to select the end diastole as opposed to end systole as the first frame because advantageously it is known that the configuration of the heart is more reproducible during this phase.
According to another aspect of the invention, there is provided a network accessible system for storing and playing back angiography images and cine angiograms. The most diagnostically relevant image frames are selected from the angiogram cine runs for each patient and stored on the network accessible system. In addition to the extraction of the diagnostically relevant images, a report including diagrammatic information for each patient is generated. The report describes the case for the patient under diagnosis. The extracted angiogram images, the report and the diagrammatic information for each patient are packaged together (or separately) and may be sent from a remote location either over the phone lines or through a dedicated network connection to a central server in the network accessible system. The central server includes web server computer software for providing secure access via the Internet to the angiographic procedure reports to authorized users (e.g. physicians) at remote locations (e.g. the office for the patient""s physician or a teaching hospital). The angiographic procedure report for a patient preferably includes one or more angiogram cine run loops, diagrammatic information and textual information. To facilitate the transmission and storage of the angiogram cine run loops for each patient, preferably the cine run loops comprise the most diagnostically relevant image frames.
In a first aspect, the present invention provides a method for generating a movie loop from a sequence of image frames, the method comprises the steps of: (a) selecting a plurality of image frames from the series wherein the selected image frames define a sequence associated with the internal anatomy; (b) registering a first image frame and a last image frame in the selected image frames; (c) wherein the step of registering the last and the first image frames comprises minimizing differences in a feature of interest appearing in the first and last image frames; and (d) forming a movie loop from the selected image frames and the registered first and last image frames, wherein the movie loop includes intermediate image frames between the first and the last image frames, the intermediate image frames being compensated for differences in the appearance of the feature of interest in the last registered image frame and the first image frame.
In a second aspect, the present invention provides a system for storing angiogram movie loops associated with one or more patients and making the angiogram movie loops available over a network, the system comprises: (a) a memory for storing the angiogram movie loops; (b) a network interface for interfacing the system to the network; (c) a command interface for processing requests from a computer connected to the network and making one or more of the angiogram movie loops available to the requesting computer.